This invention relates to devices for administration of veterinary preparations for ruminant animals.
Ruminant animals, particularly cattle and sheep, form an important group of animals which require periodic administration of veterinary medicines for the treatment and alleviation of various conditions. For example, it is often desirable to treat such animals, either therapeutically or prophylactically, with mineral or vitamin supplements, antibiotics, systemic insecticides, detergents for the relief of cattle bloat, and/or anthelmintics or other anti-parasitic agents. The repeated administration of such veterinary medicines to animals at frequent time intervals is expensive and inconvenient. There is therefore much need for a dosing system to be devised which would efficiently supply the veterinary medicine during prolonged periods of time after administration of a single preparation.
British Pat. No. 1318259 describes a number of devices for retaining slow release veterinary medicament formulations in the rumen over an extended period of time, thereby achieving the desired result. This prolonged retention in the rumen is obtained by the devices having a relatively narrow first configuration which allows the devices to be administered per os to the ruminant, and a relatively broad second configuration which the devices assume or are caused to assume in the rumen thereby hindering or preventing their passage out of the rumen. A typical example of such a device specifically described in said Pat. No. 1318259 is a plastic cylindrical capsule containing a detergent for the control of bloat in cattle. The capsule is 150 mm long and 30 mm wide (thereby allowing per os administration), and consisting of two half-cylinders hinged along one edge. The hinges are made from rubber and are biased so that the two half-cylinders spring apart in the rumen and thus become too wide to pass out through the rumen or to be regurgitated through the oesophagus. Each half-cylinder contains a gel of ethyl cellulose containing the desired anti-bloat agent which is leached from the gel by the rumen fluids over an extended period of time. The hinges are constructed so that under the rumen conditions they pull away from the half-cylinders after effective release of the agent thereby facilitating regurgitation of the fragmented device.
Other veterinary devices intended to achieve the same result are described in European patent applications Nos. 10987A and 21758A. These devices may comprise a flexible carrier sheet rolled into an open-ended tube-like configuration which is generally cylindrical, the sheet being constrained in that configuration by strips of gummed paper or similar means which are released when the preparation enters the rumen and becomes immersed in the rumen fluids. Typical dimensions of the cylinder formed by the sheet in its rolled-up condition are 3 cm diameter and 10 cm length. The preparation in its cylindrical state may be administered to the animal by means of a balling gun and enters the rumen through the oseophagus. In the rumen the constraining means become released and the sheet unrolls to an opened, relatively broad configuration in which it remains in the rumen and cannot escape. The sheet contains a medicament which is discharged into the rumen fluid over a period of time and the sheet is adapted to discharge the medicament at a predetermined rate. One such sheet is described in European patent application No. 0153070A and comprises a plastics core layer providing a matrix containing the medicament coated on its major surfaces with an inert plastics coating to form a trilaminate, the trilaminate having a pattern of perforations through which the medicament is discharged in the rumen. The rate of discharge of the medicament is determined primarily by the number and size of the perforations.
It has been found that such open-ended rolled-up sheet devices, while operating efficiently after entering the rumen, may become stuck in the oesophagus when administered to ruminants, particularly small calves, and are not ejected by the natural regurgitation action of the animal. The constraining means may then be released in the oesophagus and the sheet become unrolled so that it becomes impacted and cannot be removed. Permanent obstruction of the oesophagus in this way has serious consequences for the animal and is normally fatal.
Attempts have been made to avoid this problem by providing increased lubrication for the preparation, for example by coating it with corn oil or polyethylene glycol wax to ease its passage into the rumen. However, it has been found that impaction of the preparation in the oesophagus still occurs in a significant proportion of the animals treated.